The present invention relates to an improved control system for hydraulic positioning devices such as used in what is commonly termed setworks for setting the position of such equipment as machine tools, saws, chippers and edges utilized in the wood products industries, and various other applications. Commonly, these systems are a combination of mechanical and/or hydraulic linkages which make available a given number of set positions to the appliance they control. The present invention is especially directed to improvements in a setworks system which is totally hydraulic wherein two circuits are used, one to control the other with a follow-up function linking the two.
Prior systems of the type under consideration have been inadequate in many respects and, additionally, require quite complex and cumbersome apparatus. One particular problem has been in the nature of the apparatus needed to perform the follow-up function between the control circuit and the power circuit. In the past, some external apparatus was necessary, such as a traveling rod or operator, to follow the motion of the power cylinder so as to reset or neutralize the control linkage when a particular set position was reached. Other problems experienced with hydraulic systems are the difficulties of calibration and compensation for temperature changes and seal leakage.
The present invention seeks to alleviate the shortcomings of the prior art systems by the provision of a dual circuit hydraulic system wherein the follow-up function is accomplished by a structure internal to the double acting cylinder, thus eliminating the necessity for any push rod apparatus or the like. In addition to this advantage, a unique arrangement is provided for temperature and seal leakage compensation and recalibration. Electrical controls are also provided for the dual circuit system whereby the number and combination of sets may be easily and rapidly changed for increased flexibility.
Accordingly, the primary object of the present invention is to provide a hydraulic positioning device comprising separate control and power circuits wherein the follow-up function between the control and power circuits is accomplished by a structure completely internal to the power cylinder.
Another object of the present invention is to provide a hydraulic positioning device of the character described which may be easily calibrated to compensate for temperature changes and seal leakage.
Another object of the present invention is to provide a hydraulic positioning device of the character described which is controlled by an electrical system enabling changes to be made in the number and combination of sets in a rapid and simple manner.
These and other objects and advantages of the invention will be apparent from the following specification and claims and from the accompanying drawings wherein: